Stroke control apparatus for an hydraulic pump

ABSTRACT

A stroke control apparatus for a hydraulic pump whose amount and direction of flow can be varied, comprises an actuating element engaged with a swash plate of the pump, a spring-biassed piston movable in response to pressure at a port of the pump and a lever mechanism disposed between the piston and the actuating element. The lever mechanism comprises a pair of levers. One of the levers has a first abutment engaging the piston, a second abutment for engaging the actuating mechanism and a third abutment. The second lever has a first abutment engaging the third abutment and a second abutment for engaging the actuating element. A spring between the two levers resiliently urges the first abutment on the second lever against the third abutment and also urges the first abutment on the first lever against the piston. Movement of the piston due to increasing pressure in the pump port causes pivoting of the levers so that one or other of the second abutments moves the actuating element in a direction to reduce the stroke of the pump.

United States Patent [191 Jones Apr. 16, 1974 STROKE CONTROL APPARATUS FOR AN HYDRAULIC PUMP [75] lnventor: Brian Paul Jones, l-luyton, England [73] Assignee: JosephLucas (Industries) Limited,

Birmingham, England [22] Filed: Feb. 13, 1973 [21] Appl. No.: 332,207

[52] US. Cl. 417/222, 91/506 [51] Int. Cl. F04b 1/26 [58] Field of Search 417/222; 91/505, 506

Primary Examiner-William L. Freeh Assistant Examiner-r-Gregory Paul LaPointe Attorney, Agent, or Firm- Holman & Stern [57] ABSTRACT A stroke control apparatus for a hydraulic pump whose amount and direction of flow can bevaried, comprises an actuating element engaged with a swash plate of the pump, a spring-biassed piston movable in response to pressure at a port of the pump and a lever mechanism disposed between the piston and the actuating element. The lever mechanism comprises a pair of levers. One of the levers has a first abutment engaging the piston, a second abutment for engaging the actuating mechanism and a third abutment. The second lever has a first abutment engaging the third abutment and a second abutment for engaging the actuating element. A spring between the two levers resiliently urges the first abutment on the second lever against the third abutment and also urges the first abutment on the first lever against the piston. Movement of the piston due to increasing pressure in the pump port causes pivoting of the levers so that one or other of the second abutments moves the actuating element in a direction to reduce the stroke of the pump. I

5 Claims, 2 Drawing Figures e s L O SE J 7 3| 7 p 3O 2 ':mo 33 STROKE CONTROL APPARATUS FOR AN HYDRAULIC PUMP This invention relates to a stroke control apparatus for a hydraulic pump of the type which includes stroke varying means operable to adjust both the amount and direction of pump delivery, and has as an object to provide such an apparatus in a convenient form.

According to the invention a stroke control apparatus for a hydraulic pump of the foregoing kind, comprises (i) an actuating element engageable with a stroke varying means of the pump, (ii) a piston movable in one direction by a pressure signal derived from the pump output pressure, (iii) biasing means urging said piston in the opposite direction, (iv) a first lever having a first abutment engaging said piston, a second abutment engageable with the actuating element to urge the latter in a first direction to reduce the stroke of the pump, and a third abutment, (v) a second lever having a first abutment engaging with said third abutment and a second abutment engageable with the actuating member to urge the latter in a second direction to reduce the stroke of the pump, the arrangement being such that movement of said piston in said one direction causes the second abutments on the first and second levers to be moved in said first and second directions respectively, and (vi) means resiliently biasing said second abutments against movement by said piston.

A stroke control apparatus according to the invention will now be described by way of example and with reference to the accompanying drawings in which:

FIG. 1 is a section through the apparatus and FIG. 2 is a section on line 2-2 inFlG. 1.

' A variable stroke hydraulic pump, shown generally at 10, is of the axial piston type and includes a swash plate which can be pivoted to vary both the amount and the direction of flow of the, pump delivery. The stroke control apparatus includes a housing 1 1 in which an actuating element 12 is slidable, the element 12 being engaged with the swash plate to move the latter. The element 12 includes a pair of flanges 13, 14 which define between them a groove 15.

A piston assembly 16 is slidable in the housing 11.

Assembly 16 includes a sleeve 17 formed with a shoulder 18 and a stem 19 around which the sleeve 17 is a clearance fit. A bearing element 20 has a recess which locates on sleeve 17. Axial movement of bearing element 20 is prevented by a circlip 21 defining a shoulder on stem 19. Element 20 has a radial clearance around stem 19 and circlip 21 so as to permit limited radial movement of stem 19 relative to sleeve 17. A guide 22 extends from the housing 11, and supports a bush 23 carried on the end of stem 19. Bush 23 has a flange 23a whose rim is part-spherical form, permitting bush 23 to pivot within guide 22. A spring 24 engages the bush 23 and an end of guide 22 to bias bearing element 20 into engagement with sleeve 17 and also to urge the piston assembly 16 to the right as seen in FIG. 2. Movement of assembly 16 under the influence of spring 24 is limited by engagement of bearing element 20 with the housing 11. i

Shoulder l8 lies within a recess 25 in the housing 11.-

Recess 25 communicates with whichever of the ports of pump is at the higher pressure. Recess 25 also communicates via a spring-loaded relief valve 26 and a flow restrictor 27 with an auxiliary pisotn and cylinder unit 28 which is axially aligned with stem 19. Unit 28 also communicates via restrictor 27 and a further restrictor 29 with a low-pressure zone 30. l

A lever 31 is mounted in the housing 11 for pivotal movement about an axis 32. Lever 31 has at one end an abutment 33 which engages an end of stem 19, and at the other end an abutment 34 engageable with a face of flange 13. Lever 31 also includes a forked portion 35 which carries a ball-bearing unit 36, forming a third abutment on lever 31. A further lever 37 is mounted in housing 11 for pivotal movement about an axis 38. Lever 37 has a portion 39 which abuts bearing unit 36 and also includes an abutment 40 which is engageable with a face of flange 14. A spring 41 engages pegs 42,.

43 on levers 31, 37 respectively to bias abutment 33 against stem 19 and portion 39 against bearing unit 36, thereby urging abutments 34, 40 away from each other and from the adjacent faces of the flanges 13, 14.

A lever 44 is pivotally mounted externally of housing 11 so as to control the position of a spring-loaded link assembly 45 within the housing 11. Assembly 45 includes a stud 46 which is engaged in groove 15. Assembly 45 is of known type whereby lever 44 can be movedrelative to stud 46, in which circumstance a spring 47 of assembly 45 applies a bias to element 12, urging it to follow lever 44.

In use, the position of elemtnt 12, and hence the stroke of the pump l0, is normally controlled by lever 44, which can move element 12 in either direction from the neutral position shown in FIG. 1. However, as pump delivery pressure rises piston assembly 16 is moved to the left, as seen in FIG. 2, as a result of pressure in recess 25 acting-on shoulder 18. Resultant movement of lever 31 causes abutments 34, 40 to move inwards and, by engagement with flanges 13, 14 respectively, either to urge element 12 towards a central position to reduce the stroke of pump 10 or to limit movement of element 12 by lever 44. The force exerted by spring 47 is such that it will always be overridden by movement of piston assembly 16.

Abutment 33 exerts, as a result if friction during pivoting of the lever 31, a transverse forceon stem 19. Circlip 21 can slide relatively freely on element 20 by vir tue of the clearance between sleeve 17 and stem 19, and also by virtue of the freedom of bush 23topivot within guide 22. The effect of spring 24 on bush 23 tends to urge stem 19 to a centralposition within sleeve 17. Transverse forces are thereby transmitted to sleeve 17 only to limited extent. Stiction between sleeve 17 and housing 11, due to relative displacement of their axes, is reduced thereby. l-lystereses is therefore reduced.

A rise in pressure in recess 25 above a predetermined level causes valve 26 to lift and position cylinder unit 28 to operate immediately to destroke pump 10 completely. In normal operation however, the control apparatus does not act todestroke the pump completely. Angular movement of lever 31 is thus normally small and so, therefore, is transverse movement of abutment 33 relative to sleeve 17. Clearance between sleeve 17 and stem 19 may therefore be relatively small.

I claim:

l. A stroke control apparatus for a hydraulic pump provided with stroke varying means operable to adjust the amount and direction of pump delivery, said apparatus comprising (i) an actuating element engageable with the stroke varying means, (ii) a piston movable in one direction by a pressure signal derived from the pump output pressure, (iii) biasing means urging said piston in the opposite direction, (iv) a first lever having a first abutment engaging said piston, a second abutment engageable with the actuating element to urge the latter in a first direction to reduce the stroke of the pump, and a third abutment, (v) a second lever having a first abutment engaging with said third abutment, and a second abutment engageable with the actuating member to urge the latter in a second direction to reduce the stroke of the pump, the arrangement being such that movement of said piston in said one direction causes the second abutments on the first and second levers to be moved in said first and second directions respectively, and (vi) means resiliently biasing said second abutments against movement by said piston.

2. A stroke control apparatus as claimed in claim 1, wherein pivots provided for the first and second levers are disposed relative to each other so that the second abutments on the first and second levers move towards one another whilst moving in the first and second directions.

3. A stroke control apparatus as claimed in claim 1, wherein the third abutment on the first lever comprises a rotatable bearing unit against which the first abutment of the second lever is engaged for sliding movement relative thereto.

4. A stroke control apparatus as claimed in claim 1, wherein said biasing means comprises a spring disposed between and attached to the levers so as to urge resiliently the first abutment on the second lever into engagement with the third abutment on the first lever.

5. A stroke control apparatus as claimed in claim 1, wherein a further lever is provided with spring-loaded link assembly whereby it is connected with the actuating element to control the stroke of the pump in use, the spring-loaded link assembly being adapted to be over-ridden by the assembly of piston and first and second levers. 

1. A stroke control apparatus for a hydraulic pump provided with stroke varying means operable to adjust the amount and direction of pump delivery, said apparatus comprising (i) an actuating element engageable with the stroke varying means, (ii) a piston movable in one direction by a pressure signal derived from the pump output pressure, (iii) biasing means urging said piston in the opposite direction, (iv) a first lever having a first abutment engaging said piston, a second abutment engageable with the actuating element to urge the latter in a first direction to reduce the stroke of the pump, and a third abutment, (v) a second lever having a first abutment engaging with said third abutment, and a second abutment engageable with the actuating member to urge the latter in a second direction to reduce the stroke of the pump, the arrangement being such that movement of said piston in said one direction causes the second abutments on the first and second levers to be moved in said first and second directions respectively, and (vi) means resiliently biasing said second abutments against movement by said piston.
 2. A stroke control apparatus as claimed in claim 1, wherein pivots provided for the first and second levers are disposed relative to each other so that the second abutments on the first and second levers move towards one another whilst moving in the first and second directions.
 3. A stroke control apparatus as claimed in claim 1, wherein the third abutment on the first lever comprises a rotatable bearing unit against which the first abutment of the second lever is engaged for sliding movement relative thereto.
 4. A stroke control apparatus as claimed in claim 1, wherein said biasing means comprises a spring disposed between and attached to the levers so as to urge resiliently the first abutment on the second lever into engagement with the third abutment on the first lever.
 5. A stroke control apparatus as claimed in claim 1, wherein a further lever is provided with spring-loaded link assembly whereby it is connected with the actuating element to control the stroke of the pump in use, the spring-loaded link assembly being adapted to be over-ridden by the assembly of piston and first and second levers. 